J. Requies

Furfural production from xylose using sulfonic ion-exchange resins (Amberlyst) and simultaneous stripping with nitrogen

The aim of this work deals with the development of new approaches to the production of furfural from xylose. It combines relatively cheap heterogeneous catalysts (Amberlyst 70) with simultaneous furfural stripping using nitrogen under semi-batch conditions. Nitrogen, compared to steam, does not dilute the vapor phase stream when condensed. This system allowed stripping 65% of the furfural converted from xylose and almost 100% of selectivity in the condensate. Moreover, high initial xylose loadings led to the formation of two water-furfural phases, which could reduce further purification costs. Constant liquid-vapor equilibrium along stripping could be maintained for different xylose loadings. The modeling of the experimental data was carried out in order to obtain a liquid-vapor mass-transfer coefficient. This value could be used for future studies under steady-state continuous conditions in similar reaction-systems.

Furfural production from xylose + glucose feedings and simultaneous N2-stripping

The current furfural manufacturing process is based on homogeneous catalysts as well as steam as the stripping agent. Novel xylose-dehydration research studies include heterogeneous catalysts with high acidity and tailored selectivity. This work aims to evaluate the effect of additional glucose with the xylose feeding during simultaneous N2-stripping of furfural catalyzed by ion-exchange resins. Given the low batch performance of Amberlyst 70, the N2-stripping data showed high furfural yields and selectivity in the condensate stream. The different continuous feeding configurations showed that xylose/glucose ratios similar to the real pentosan-rich biomass could be fed achieving furfural yields of 75% at 200 °C. Moreover, the proposed study serves as a preliminary study to achieve high xylose conversion and relatively low glucose dehydration rates, showing its potential as a possible future process for the upgrading of carbohydrates to furan-based fuel additives.

Physicochemical Study of Glycerol Hydrogenolysis Over a Ni–Cu/Al 2 O 3 Catalyst Using Formic Acid as the Hydrogen Source

Glycerol hydrogenolysis to propanediols requires the use of hydrogen as reactant. One interesting option is to directly generate this hydrogen in active sites of the support using hydrogen donors, such as formic acid. The effect that the reacting pressure has on glycerol conversion and product selectivity over a Ni–Cu/Al2O3 catalyst was studied. The negative effect of decreasing the pressure was much more significant when the source of hydrogen was dissolved molecular hydrogen than when it was formic acid. X-ray photoelectron spectroscopy and temperature programmed reduction measurements were performed to understand the effect of Ni–Cu/Al2O3 reduction procedure on the catalytic activity. Semi-batch reactor studies with the Ni–Cu/Al2O3 catalyst were carried out with continuous addition of the hydrogen donor to obtain kinetic data. Langmuir–Hinshelwood type models were developed to describe the direct conversion of glycerol into propanediol, and propanediol further hydrogenolysis to 1-propanol. The model included the competitive adsorption between both glycols. These models were used to obtain valuable data for the optimization of the process.

Levulinic acid hydrogenolysis on Al2O3-based Ni-Cu bimetallic catalysts

Abstract Inexpensive γ-alumina-based nickel-copper bimetallic catalysts were studied for the hydrogenolysis of levulinic acid, a key platform molecule for biomass conversion to biofuels and other valued chemicals, into γ-valerolactone as a first step towards the production of 2-methyltetrahydrofurane. The activities of both monometallic and bimetallic catalysts were tested. Their textural and chemical characteristics were determined by nitrogen physisorption, elemental analysis, temperature- programmed ammonia desorption, and temperature-programmed reduction. The monometallic nickel catalyst showed high activity but the highest by-product production and significant amounts of carbon deposited on the catalyst surface. The copper monometallic catalyst showed the lowest activity but the lowest carbon deposition. The incorporation of the two metals generated a bimetallic catalyst that displayed a similar activity to that of the Ni monometallic catalyst and significantly low by-product and carbon contents, indicating the occurrence of important synergetic effects. The influence of the preparation method was also examined by studying impregnated- and sol-gel-derived bimetallic catalysts. A strong dependency on the preparation procedure and calcination temperature was observed. The highest activity per metal atom was achieved using the sol-gel-derived catalyst that was calcined at 450 °C. High reaction rates were achieved; the total levulinic acid conversion was obtained in less than 2 h of reaction time, yielding up to 96% γ-valerolactone, at operating temperature and pressure of 250 °C and 6.5 MPa hydrogen, respectively.

Influence of the support of bimetallic Pt-WOx catalysts on the 1,3-propanediol formation from glycerol

Three aluminium oxide materials and a HZSM‐5 zeolite were used as supports of bimetallic Pt‐WOx catalysts to establish structure–activity relationships in the glycerol hydrogenolysis reaction. The surface W density and the intimate contact between Pt and WOx were key parameters. Surface W density controls the formation of polytungstates, the only species able to produce the weak Brønsted acidity that is required to produce 1,3‐propanediol selectively. The comparison between the HZSM‐5 and the Al2O3 supports demonstrated that an increment of the medium Brønsted acidity is detrimental for the selective 1,3‐propanediol formation as it promotes reactions that yield 1‐propanol and propane. An increase of the dispersion of Pt on the Pt/WOx/Al2O3 catalysts led to higher glycerol conversions but also promoted the hydrogenolysis routes that lead to 1,2‐ and 1,3‐propanediol similarly. On the contrary, an increase of the Pt metal content favoured the hydrogenolysis route that leads to 1,3‐propanediol significantly. A more intimate contact between Pt and WOx promoted the hydrogenation of the intermediate carbocation, formed and stabilised on a polytungstate active site, into 1,3‐propanediol.

Natural and synthetic iron oxides for hydrogen storage and purification

In this paper, the hydrogen storage capacity of some synthetic and natural iron oxides is presented. The results of the activity tests and characterization techniques of natural and synthetic iron oxides (N2 adsorption–desorption isotherms, temperature-programmed reduction, X-ray diffraction, and plasma atomic emission spectroscopy) suggest that the use of chromium on iron oxide systems improved their hydrogen storage capacity. This is related to the capacity of chromium to modify the iron oxide reduction profile when Cr was incorporated. A direct reduction from Fe3O4 to Fe was observed as the mechanism for H2 storage. In addition, natural oxides as commercial Superfine and Densinox-L oxides are proved to be suitable materials to store and purify H2 due to their high stability during different cycles of reduction and oxidation. The best results among the natural ones were Densinox-L and among the synthetic ones Fe–10Cr.

13 – Hydrogen purification methods: Iron-based redox processes, adsorption, and metal hydrides

One of the keys in the possibility of employing hydrogen as an energy vector in the future is its purification. There are many techniques to purify hydrogen from a mixture, and these processes present different advantages and disadvantages. Therefore, there are many studies that develop new processes for hydrogen purification. This review summarizes the progress of some of them, as the most recent advances on redox reactions, metal hydrides, and adsorption for hydrogen purification. This review considers fundamental aspects including the thermodynamic and kinetic viewpoints, the potential of hydrogen purification processes, the main advantages and disadvantages to purify this hydrogen, the new materials employed in these processes, and the system design features.One of the keys in the possibility of employing hydrogen as an energy vector in the future is its purification. There are many techniques to purify hydrogen from a mixture, and these processes present different advantages and disadvantages. Therefore, there are many studies that develop new processes for hydrogen purification. This review summarizes the progress of some of them, as the most recent advances on redox reactions, metal hydrides, and adsorption for hydrogen purification. This review considers fundamental aspects including the thermodynamic and kinetic viewpoints, the potential of hydrogen purification processes, the main advantages and disadvantages to purify this hydrogen, the new materials employed in these processes, and the system design features.

Production of Furanic Biofuels with Zeolite and Metal Oxide Bifunctional Catalysts for Energy-and Product-Driven Biorefineries

In the last years, research on the transformation of biomass into different compounds has grown significantly with the motivation being to reduce the dependency of oil and to develop of sustainable and environmental friendly energy sources. In this context biomass appears to be as the only renewable source of carbon that is able to provide a substitute for fossil fuels. In the near future, bio-refineries, in which biomass is catalytically converted into pharmaceuticals, agricultural chemicals, plastics and transportation fuels will take the place of current petrochemical plants. Among the transportation fuels, furanic biofuels as 2,5-dimethylfuran (DMF) and 2-methylfuran (2-MF) have good performance as a fuel for direct injection spark ignition type engines without important modifications of the engine. The transformation of biomass into furanic biofuel compounds takes place via 5 hydroxymethylfurfural (HMF) in the case of the DMF and 2-MF; in the case of the 2-MF it can be also produced from furfural (FF) via furfuryl alcohol (FOL). In these reactions it is necessary to employ of bifunctional catalysts for the hydrogenolysis. Metals are required to fix the hydrogen reaction and sometimes for the C–O and C–C bonds cleavage and the acid-base supports of the dehydration, for the C–C and C–O bonds scissions. This chapter provides an overview of current methods for converting biomass to furanic biofuels with zeolite and metal oxide bifunctional catalysts. The chapter provides state-of-the-art overview on furanic biofuel production from biomass with a brief description of the DMF production process and the 2-MF production process. Use of different bifunctional catalysts for the DMF production process and the 2-MF production process is described. The influence of the support and that of different metals will be discussed along with properties of the bifunctional catalysts like metal dispersion, catalysts acidity and operating conditions. Finally, the use of different solvents to improve the yield of biofuels will be analyzed.